Many coating properties such as colour intensity, opacity and gloss depend upon the extent of aggregation or flocculation of pigment particles (or other particulate materials) within the coating. Colour is normally introduced into a coating formulation by addition of a pigment dispersion in solvent containing a high concentration of pigment. The pigment dispersion is generally produced by one of a variety of milling techniques to break up the aggregates of pigment particles and reduce the average particle size. Milling is often carried out in the presence of some polymeric material which is present to stabilize the dispersion and minimize flocculation of the dispersed particles.
It can often be advantageous to be able to use one colour concentrate for letdown into a variety of different binder systems. However, the polymeric material present in the colour concentrate can give rise to problems if it is not compatible with the coating binder. For example, when nitrocellulose is utilised as a pigment grinding medium in a polyamide binder system, there may be compatibility problems leading to reduced gloss and colour strength.
U.S. Pat. No. 6,406,143 discloses a graft copolymer of styrene-maleic anhydride reacted with a polyetheramine. The graft copolymer is described as suitable for use as an ink-jet dispersant.
U.S. Pat. Nos. 5,705,603, 5,391,632; and European Patent applications EP 324 547 A2, and EP 606 055 B1, all disclose a polyetheramine copolymer containing α,β-unsaturated dicarboxylic acids or anhydrides. The dicarboxylic acids or anhydrides groups are reacted such that they contain 20-80 mole percent of a mixture of (i) unreacted anhydrides, imides, amides, half-acid-amides. The imides and amides are derived from an alkyl amine containing 6 to 40 carbon atoms.
Japanese Patent publication JP 2006028252 A (published on Feb. 2, 2006, and assigned to Ajinomoto Co. Inc.) discloses an amino-group containing maleic acid copolymer useful as a dispersant. The copolymer contains a ratio of constituent (A) to constituent (B) of 1:3 to 3:1.
Therefore, there is a need for pigment dispersants which can generate stable colour concentrates and provide acceptable or improved coating properties when used in a range of different ink and coating binders such as nitrocellulose, polyamide and polyurethane.